The present invention relates to a linear motor, more particularly relates to a linear motor able to use a stacked member comprised of a plurality of magnetic sheets stacked together as a stator (platen).
Explaining the principle of a Sawyer linear motor, as shown in FIG. 12, it is comprised of a platen (stator) 10 comprised of a magnetic thick plate on whose surface is repeatedly formed platen dots D at a spatial period of the dot pitch P and a movable member (traveling member) 20 comprised of a permanent magnet M for generating a bias magnetic flux, first and second yokes Y1 (Y2) bonded to the magnetic pole surface to be arranged in parallel to the direction of advance and provided with first and second branched magnetic path legs A and Axe2x80x2 (B and Bxe2x80x2), series-connected first and second A-phase excitation coils CA and CAxe2x80x2 wound around the first and second branched magnetic path legs A and Axe2x80x2 of the first yoke Y1, series-connected first and second B-phase excitation coils CB and CBxe2x80x2 wound around the first and second branched magnetic path legs B and Bxe2x80x2 of the second yoke Y2, and two pole teeth (projecting poles) KA and KAxe2x80x2 (KB and KBxe2x80x2) formed at each of the bottom ends of the first and second branched magnetic path legs A and Axe2x80x2(B and Bxe2x80x2) and arranged in the direction of advance at intervals of xc2xd of the dot pitch P. Here, each branched magnetic path leg may be formed with only one pole tooth, but in the event of several, the spatial phase held with respect to the closest dots of the platen dots D is the same. Further, the interval between the first branched magnetic path leg A (B) and second branched magnetic path leg Axe2x80x2(Bxe2x80x2) is set so that the spatial phases with respect to the closest dots are shifted in the direction of advance by exactly P/2. Further, the interval between the second branched magnetic path leg Axe2x80x2 and the first branched magnetic path leg B is set so that the spatial phases with respect to the closest dots are shifted in the direction of advance by exactly P/4.
The movable member 20 has a pressurized air ejection port and floats slightly above the surface of the platen 10 by blown pressurized air. As shown in FIG. 12A, if a B-phase current of the illustrated polarity is flown through only the terminals of the first and second xcex2-phase excitation coils CB and CBxe2x80x2 of the second yoke Y2, not only the bias magnetic flux due to the permanent magnet M, but also the alternating magnetic flux due to the second excitation coil CBxe2x80x2 are superposed and strengthened to generate a concentrated magnetic flux portion a in the air gap between the pole teeth KBxe2x80x2 of the second branched magnetic path leg Bxe2x80x2 and the closest dots D1 and D2 and strongly magnetically draw the pole teeth KBxe2x80x2 to the closest dots D1 and D2. Also, an alternating magnetic flux is applied to the pole teeth CB of the first branched magnetic path leg B in a direction canceling out the bias magnetic flux, so an extinguished magnetic flux portion b is formed. On the other hand, the magnetic flux comprised of the concentrated magnetic flux from the second branched magnetic path leg Bxe2x80x2 of the second yoke Y2 branched via the inside of the platen 10 passes through the first and second branched magnetic path legs A and Axe2x80x2 of the first yoke Y1, but the pole teeth KA of the fist branched magnetic path leg A are delayed in the direction of advance by exactly P/4 with respect to the closest dots D15 and D14. Therefore, the closest dots D15 and D14 pull the pole teeth KA in the direction of advance by one branched magnetic flux and the pole teeth KAxe2x80x2 of the second branched magnetic path leg Axe2x80x2 proceed in the direction of advance by exactly P/4 with respect to the closest dots D10 and D9 due to the other branched magnetic flex Accordingly, the closest dots D10 and D9 pull the pole teeth KAxe2x80x2 in a direction opposite to the direction of advance. Therefore, the thrust in the direction of advance and the pullback force in the reverse direction match each other perfectly and the first yoke Y1 as a whole is balanced. That is, a thrust branched magnetic flux portion d is generated in the air gap between the pole teeth KA of the first branched magnetic path leg A and the closest dots D15 and D14, while a pullback force branched magnetic flux portion c is generated in the air gap between the pole teeth KAxe2x80x2 of the second branched magnetic path leg Axe2x80x2 and the closest dots D10 and D9, so the first yoke Y1 itself becomes a stable point of the magnetic attraction potential.
Next, as shown in FIG. 12B, if an A-phase current of the illustrated polarity is supplied to only the terminals of the first and second A-phase excitation coils CA and CAxe2x80x2 of the first yoke Y1, the air gap between the pole teeth KA of the first branched magnetic path leg A and the closest dots D15 and D14 switches from what had been the thrust branched magnetic flux portion d immediately before to the concentrated magnetic flux portion a comprised of the bias magnetic flux plus the alternating magnetic flux from the second excitation coil CA superposed, while the pole teeth KAxe2x80x2 of the second branched magnetic path leg Axe2x80x2 switch from the pullback branched magnetic flux portion c to the extinguished magnetic flux portion b, so the closest dots D15 and D14 strongly magnetically draw the pole teeth KA and advancing thrust occurs at the movable member 20. On the other hand, a branched magnetic flux to form the concentrated magnetic flux at the first branched magnetic path leg A of the first yoke Y1 through the inside of the platen 10 passes through the first and second branched magnetic path legs B and Bxe2x80x2 of the second yoke Y2. The pole teeth KB of the first branched magnetic path leg B switch from the extinguished magnetic flux portion b to the thrust branched magnetic flux portion d, while the pole teeth KBxe2x80x2 of the second branched magnetic path leg Bxe2x80x2 switch from the concentrated magnetic flux portion a to the pullback branched magnetic flux portion c. Therefore, due to the switching of the two-phase current, the movable member 20 advances by exactly P/4, if including the excitation patterns of FIGS. 12C and 12D, with a two-phase current, there are four excitation patterns of the excitation coils, so by one round of the excitation patterns, the movable member 20 advances four times and proceeds by exactly one pitch worth of distance. In the process of the switching of the two-phase current, a thrust force is generated at the pole teeth moving from the thrust branched magnetic flux portion d to the concentrated magnetic flux portion a.
To realize a planar linear motor having a movable member which moves planarly in the Y-axis and Y-axial direction using such a Sawyer linear motor, for example, as seen in Japanese Unexamined Patent Publication (Kokai) No. 9-261944, as shown in FIG. 13 and FIG. 14, there are provided a platen 10 formed on the platen surface with square-top platen dots D arranged in a matrix and a composite movable member comprised of X-axis movable members 20X having stripe-shaped projecting pole teeth KA and KAxe2x80x2 (KB and KBxe2x80x2) parallel to the Y-axis and able to move in only the X-axial direction and Y-axis movable members 20Y having stripe-shaped projecting pole teeth KA and KAxe2x80x2 (KB and KBxe2x80x2) parallel to the X-axis and able to move in only the Y-axial directionxe2x80x94all connected by a support plate 30 in an in-planar perpendicular relationship.
Further, to reduce the vibration or pulsation of the movable members 20X (20Y) during the advance, as shown in FIG. 15, the yokes Y1 and Y2 may be given three branched magnetic path legs, the mutually independent phase excitation coils CU, CV, and CW (CUxe2x80x2, CVxe2x80x2, and CWxe2x80x2) wound around the branched magnetic path legs U, V, and W (Uxe2x80x2, Vxe2x80x2, and Wxe2x80x2), and a three-phase current supplied to these coils.
As a field of use of the above planar linear motor, for example, there is known a device mounting system providing a movable member moving planarly at the bottom surface of a platen held suspended down with an actuator for sliding in the normal direction of the bottom surface of the platen while holding an electronic device and inserting the electronic device into a through hole etc. of a substrate arranged under the platen.
The platen serving as the stator essential for the planar linear motor is formed on its surface with platen dots arranged in a matrix etc., so is comprised of a single thick plate magnetic material (thick steel plate) formed of a block material. Therefore, if this thick plate magnetic material is used as the platen, an eddy current naturally occurs due to the magnetic flux passing through the inside of the platen, so the AC magnetizing characteristic is poor and the power loss (iron loss) large and therefore it is difficult to obtain a high speed, high thrust force movable member and a large current capacity is required. As will be understood from the characteristic curve xcex1 of the dependency of the thrust force versus speed shown in FIG. 16, the higher the frequency the driving periodic current (current pulse) is made and the higher the speed of the advance, the more rapidly the thrust force falls and the much worse the efficiency (speedxc3x97thrust force/power consumption) becomes.
The present inventors took note of the fact that it is possible to suppress the occurrence of the eddy force and realize a high speed, high thrust, and high efficiency planar linear motor by using a stacked member comprised of a plurality of magnetic sheets (for example, a thickness of not more than 1 mm), using the parallel sheet edge surfaces of the stacked member (surface where edges of plurality of sheets appear in parallel) as the platen, and forming the platen dots arranged in a matrix by etching etc. the platen surface. Since an eddy current does not easily pass through the stacked interfaces (joined surfaces) of the magnetic sheets, the current resistance becomes higher and occurrence of an eddy current can be suppressed, so it is expected to be possible to realize a high speed, high thrust, high efficiency planar linear motor.
By making the row of pole teeth of a monoaxial movable member and the row of closest platen dots facing the same match and making the concentrated magnetic flux portion, extinguished magnetic flux portion, and branched magnetic flux portion (thrust, branched magnetic flux portion and pullback branched magnetic flux portion) move in a cyclic manner along the row direction in the magnetic circuit formed in the plane including the two rows, the monoaxial movable member advances along the row direction, so when the direction of arrangement of the pole tooth row of the monoaxial movable member and row of closest dots is the sheet edge direction of the magnetic sheets, the magnetic circuit for the advancing magnetic flux is formed in the thicknesses of the magnetic sheets in parallel to the joined surfaces, so advance of a monoaxial movable member in the sheet edge direction becomes possible and the above advantages can be obtained.
The magnet flux in the stacked member, however, is refracted or blocked at the joined surfaces and the magnetic resistance is high, so it is not actually possible to form a magnetic circuit for an advancing magnetic flux along the normal direction of the joined surfaces and advance of the monoaxial movable member in the normal direction of the joined surfaces (direction perpendicular to the sheet edge direction) is impossible. Therefore, up until now, everyone has given up on development of a planar linear motor using a stacked member as a platen.
Therefore, in view of the above problem, the object of the present invention is to realize a monoaxial movable member giving thrust in the normal direction of the joined surfaces of a stacked member and thereby enabling utilization of the stacked member of the magnetic sheets as a platen and provide a high speed, high thrust, high efficiency linear motor.
To solve the above problem, the means devised by the present invention is to form a magnetic circuit for generating an advancing magnetic flux (concentrated magnetic flux and branched magnetic flux) for the movable member along the sheet edge direction of the stacked member and causing magnetic coupling between one set of pole teeth of the movable member and the platen dots in the normal direction of the joined surfaces of the stacked member by arranging staggered one set of pole teeth in a predetermined spatial phase relationship within one pitch in the normal direction of the joined surfaces.
That is, the present invention provides a linear motor provided with a platen having a platen surface formed with a plurality of platen dots arranged in a matrix and on X-axis movable element having an pole tooth pattern having a set of at least 2n (where n is an integer of 2 or more) pole teeth for generating on advancing magnetic flux with the closest dots among the platen dots, wherein the platen has the parallel sheet edge surfaces of the stacked member comprised of the plurality of magnetic sheets stacked together as the platen and wherein the 2n number of magnetic teeth of the pole tooth pattern are arranged laterally in equal spatial phase relation with the closest dots arranged in the sheet edge direction (Y-direction) of the magnetic sheets. Further, the 2n number of pole teeth of the pole tooth pattern are arranged staggered within one dot pitch (P) in the normal direction of the joined surfaces of the magnetic sheets. The spatial phase held with respect to the closest dot arranged in the normal direction is shifted by increments of the spatial phase difference (P/2n). That is, the spatial phases held by the pole teeth with respect to the closest dots, when any spatial phase is p, are assigned as pxe2x88x92P/4, p, p+P/4, and p+P/2 when n=2, as pxe2x88x92P/3, pxe2x88x92P/6 p, p+P/6, p+P/3, and p+P/2 when n=3, and as pxe2x88x923P/8, pxe2x88x92P/4, pxe2x88x92P/8, p, p+P/8, p+P/4, p+3P/8, and p+P/2 when n=4.
According to this configuration, since all of the 2n number of pole teeth of the pole tooth pattern hove spatial phases held with respect to the closest dots arrayed in the sheet edge direction (Y-axial direction) of magnetic sheet, the X-axis movable member does not receive a thrust force to the Y-axial direction, but the 2n number of pole teeth of the pole pattern of the X-axis movable member are arranged staggered shifted in phase in one dot pitch P in the normal direction of the joined surfaces of the magnetic sheets, so the magnetic circuit for the advancing magnetic flux is formed along the sheet edge direction of the stacked member. Further, the 2n number of pole teeth of the pole pattern of the X-axis movable member have spatial phases held with respect to the closest dots arranged in the normal direction of the joined surface of the magnetic sheets shifted by exactly increments of the spatial phase difference (P/2n), so magnetic couplings are caused with the closest dots arranged in the X-axial direction, the thrust force in the X-axial direction acts successively on the 2n number of pole teeth of the pole tooth pattern laterally elongated in the Y-axial direction due to the cycle of combination of the concentrated magnetic flux and branched magnetic flux, and the X-axis movable member moves translationally in the X-axial direction due to so-called xe2x80x9ccrawling motionxe2x80x9d.
In this way, since it is possible to realize a monoaxial movable member giving thrust in the normal direction of the joined surfaces of the stacked member, it is possible to realize utilization of a stacked member of magnetic sheets as a platen and possible to provide a high speed, high thrust, high efficiency linear motor. The thrust force acts on the pole teeth switching from the branched magnetic flux to the concentrated magnetic flux, but the branched magnetic flux and concentrated magnetic flux occur at pole teeth of different yokes, so a rotational moment acting on the X-axis movable member occurs alternately in the forward and reverse directions. The higher the speed of movement, however, the smaller the ratio of the rotational vibration with respect to the speed of travel.
The pole teeth where the extinguished magnetic flux portion occurs differs the most, that is, half of a pitch, among the pole teeth from the pole teeth where the concentrated magnetic flux occurs. In the case of a platen using a magnetic sheet having a thickness of within half a pitch, the magnetic circuit formed along the sheet edge direction inherently finds it hard to hold magnetic couplings with pole teeth where extinguished magnetic flux parts occur, so there is no need to generate an alternating magnetic flux of a strength exactly extinguishing the bias magnetic flux and the degree of freedom of design is increased. In the case of a two-phase linear motor, the spatial phase difference held by an pole tooth of the concentrated magnetic flux portion and the pole teeth of the pair of branched magnetic fluxes with respect to the closest dots is P/4, while the spatial phase difference held by the pole tooth of one branched magnetic flux and the pole tooth of the other branched magnetic flux is P/2. In the case of a three-phase linear motor, the spatial phase difference held by an pole tooth of the concentrated magnetic flux and the pole teeth of the pair of branched magnetic fluxes with respect to the closest dots is P/6, while the spatial phase difference of the pole tooth of one branched magnetic flux and the pole tooth of the other branched magnetic flux with respect to the closest dots is P/3. Therefore, in the case of a three-phase linear motor, it is preferable to use a magnetic sheet with a thickness of not more than ⅓ of the pitch. In general, in the case of an n-phase linear motor, it is preferable to use a magnetic sheet having a thickness of not more than 1/n of the pitch. The greater the number of phases, the thinner the sheets. With three or more phases, magnetic coupling is hard to occur at both of the pair of pole teeth where the weak branched magnetic flux occurs, so the excess magnetic coupling consumed in stopping the progression is cut off and can be put to use in the thrust force of the progression. Rather, a higher efficiency can be expected from the X-axis movable member giving thrust in the perpendicular direction compared with the Y-axis movable member giving thrust in the sheet edge direction. Therefore, the present invention is not limited to the X-axis movable member of a 2D planar linear motor and has sufficient value of use as a one-dimensional linear motor comprised of a platen using a stacked member and a monoaxial movable member giving thrust in a normal direction of the joined surfaces of the stacked member. Further, since the platen is a stacked member of magnetic sheets, it may be a stacked member with plastic or other nonmetallic materials sandwiched between dots in the X-axial direction. Further, it is not necessary to provide recesses between the dots. The platen can also be fabricated easily. Further, the leakage magnetic flux can be reduced and a higher efficiency can be contributed to.
Note that the spatial phase relationship between the set of poles of the movable member side and the set of closest dots of the platen side is relative, so instead of giving a staggered arrangement in the phase relationship among the pole teeth of the movable member, it is also possible to give a staggered arrangement in the phase relationship among the platen dots arranged in the X-axial direction of the platen side.
When the X-axis movable member has a group of patterns comprised of a pole tooth pattern arranged repeatedly in the normal direction of the joined surfaces, it is possible to obtain stable travel and high output of the X-axis movable member.
A pair of patterns are formed comprised of the above pole tooth pattern as a first pole tooth pattern and a second pole tooth pattern separated in the normal direction from the first pole tooth pattern. The staggered arrangement of the first pole tooth pattern and the staggered arrangement of the second pole pattern are line symmetric about the X-direction line passing through the pattern center. Both staggered arrangements are in spatial phase relationship held with respect to the closest dots arranged in the normal direction of the joined surfaces of the magnetic sheets of the first pole tooth pattern and the second tooth pattern, respectively. Since a forward and reverse rotational moment simultaneously act on the X-axis movable member, the rotational moments are canceled out and it is possible to eliminate rotational vibration.
When the X-axis movable member has a group of patterns comprised of the first pole pattern and second pole pattern arranged alternately repeatedly in the normal direction of the joined surfaces, it is possible to again obtain stable travel and high output of the X-axis movable member.
It is preferable to configure the planar linear motor by the above X-axis movable member and Y-axis movable member moving in the sheet edge direction of the magnetic sheets connected in an in-plane perpendicular relationship, but here two X-axis movable members and two Y-axis movable members are arranged diagonally with respect to the center point of the plane of the composite movable member and arrange the pole tooth pattern of one X-axis movable member and the pole tooth pattern of the other X-axis movable member fine symmetrically with respect to the X-direction line passing through the center point of the plane. The rotational moment about the center point of the plane of the composite movable member acts simultaneously in the forward and reverse directions, the rotational moments are canceled out, and the rotational vibration of the composite movable member as a whole can be eliminated and therefore stable travel in the X-axial direction and Y-axial direction can be realized from low speed travel to high speed travel.